Cytomegalovirus (CMV) infection is highly prevalent in transplant patients, especially in those submitted to a more intense immunosuppression. We monitored CMV infection in 34 patients during 60 days after antilymphocyte therapy without CMV prophylaxis. Six patients received sirolimus and 28 received no sirolimus as immunosuppression. During 60 days of follow-up time, 24/28 (86%) patients who did not use sirolimus developed CMV infection at a mean time of 32.43+/-13.67 days after antilymphocyte treatment. In contrast, no patient on sirolimus had CMV infection during the same follow-up (p<0.001). During a further 4-month follow-up, six patients on sirolimus-free therapy had recurrence of CMV, 46.5+/-18.5 days after the first episode. During this same period, one patient receiving sirolimus had one positive cell for CMV antigenemia, 169 days after antilymphocyte therapy. In conclusion, the use of sirolimus significantly reduced the incidence of CMV infection in patients treated with antilymphocyte antibodies.